The present invention relates to a novel positive-working photosensitive resin composition or, more particularly, to a positive-working photosensitive resin composition having high photosensitivity and excellent storage stability capable of giving a patterned photoresist layer which is excellent in the film thickness retention by development, orthogonality of cross sectional profile of line patterns, resolution and heat resistance so as to be useful as a photoresist composition for the ultra-fine patterning works on a substrate in the manufacture of various kinds of semiconductor devices such as ICs, LSIs and the like.
As is well known, the process of photolithographic patterning is widely practiced in the manufacturing process of semiconductor devices such as ICs, LSIs and the like. In the photolithographic patterning work, a layer of a photoresist composition is formed on the surface of a substrate such as a semiconductor silicon wafer and the photoresist layer is exposed pattern-wise to actinic rays such as ultraviolet light through a transparency mask bearing the desired pattern for the semiconductor device to form a latent image of the pattern which is then developed by using a developer solution to give a patterned resist layer to serve as a protecting mask for the substrate surface in the subsequent treatment of etching and the like. Photoresist compositions are classified into negative-working ones and positive-working ones depending on the behavior of the photosensitive resin composition against irradiation with actinic rays. Positive-working photoresist compositions of the most widely used type are those comprising an alkali-soluble novolac resin as the film-forming constituent and a photosensitizing agent which is a quinone diazide group-containing compound or, in particular, an aromatic polyhydroxy compound esterified with naphthoquinone-1,2-diazide sulfonic acid (see, for example, U.S. Pat. No. 4,377,631 and Japanese Patent Kokai No. 62-35349, No. 1-142548 and No. 1-179147).
It is a trend noteworthy in the technology of semiconductor devices in recent years that the density of integration in a semiconductor device is rapidly increasing year by year requiring an extremely fine photolithographic patterning work with a fineness of as fine as 1.0 .mu.m or even finer in the manufacture of VLSIs and the like. Needless to say, this requirement for fineness can be achieved necessarily as a result of the improvement in the positive-working photoresist composition used therefor, in particular, in respects of the high photosensitivity, film thickness retention by the development treatment, orthogonality of the cross sectional profile of the line pattern, resolution and heat resistance of the patterned resist layer as well as the storage stability of the photosensitive resin composition to contribute to the productivity of the photolithographic process.
None of the prior art positive-working photoresist compositions, however, can meet all of the above mentioned requirements. For example, the film thickness retention by development is generally low in the prior art compositions so that it is a difficult matter to obtain a high contrast of the reproduced image pattern. Along with the increased fineness in the resist pattern, furthermore, the cross sectional profile of the line pattern has a wavy side line, which should desirably be orthogonally straight, as a trend while such a patterned resist layer can no longer work satisfactorily as a protecting mask, for example, in etching.
Several proposals have also been made to formulate a positive-working photoresist composition with various photosensitizing compounds in combination with an object to obtain further enhanced photosensitivity of the composition. Although the photosensitivity of the composition can be increased by increasing the content of photosensitizers, drawbacks are sometimes caused thereby that the storage stability of the composition is decreased and the heat stability of the resist layer after patterning is decreased.